One conventional data storage system includes a storage processor, an array of magnetic disk drives and a backup power supply. The storage processor carries out a variety of data storage operations on behalf of an external host device (or simply host). In particular, the storage processor temporarily caches host data within its storage cache and, at certain times, de-stages that cached data onto the array of magnetic disk drives. If the data storage system is set up so that it acknowledges write requests from the host once the data reaches the storage cache rather than once the data reaches the array of magnetic disk drives, the host will enjoy shorter transaction latency.
Some data storage systems employ backup power supplies (e.g., uninterrupted power supplies) to prevent the loss of data from the storage caches in the event of power failures. For example, suppose that such a data storage system fails to receive power from a main power feed (e.g., power from the street) during operation. In such a situation, a set of backup power supplies provides reserve power to the storage processor and to the array of magnetic disk drives for a short period of time (e.g., 30 seconds). During this time, the storage processor writes the data from its storage cache onto a dedicated section of the magnetic disk drives called a “vault” so that any data which has not yet been properly de-staged is not lost. Once power from the main power feed returns, the storage processor loads the data from the magnetic disk drive vault back into the storage cache. At this point, the data storage system is capable of continuing normal operation.
It should be understood that some data storage systems include two storage processors for high availability (e.g., fault tolerant redundancy, higher throughput, etc.). Furthermore, some data storage systems position arrays of magnetic disk drives within enclosures which are separated from other enclosures holding the storage processors. These data storage systems typically rely on an external backup power supply for each storage processor and the array of magnetic disk drives that contain the vault. Typically the backup power supplies for the storage processors and the magnetic disk drives communicate with the various components of the data storage system through external cables in order to properly coordinate their operations.